• Tribology and Lubricants
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• v.36 no.6
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• pp.315-319
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• 2020

In various fields, several studies based on carbon nanotubes (CNTs) have been conducted. The results of previous studies, wherein CNT coatings have been incorporated as solid lubricants, demonstrate that the friction and wear characteristics of CNT coatings can be improved through the absorption/dispersion of the contact pressure by controlling the stiffness of the nanomesh structure comprising CNT strands. In this study, the friction and wear characteristics of the following are compared: CNT coating formed by spin coating of CNT solution, compressed CNT coating, and compressed/heated CNT coating (wherein CNT strands are squeezed through compression and/or heating). It is observed that the friction coefficient of the CNT coating having the largest number of voids between the CNT strands is significantly lower than those of the compressed CNT coating and the compressed/heated CNT coating. The wear tracks of the compressed CNT coating and the compressed/heated CNT coating indicate that some parts become torn or adhere into a lump. However, in the case of the CNT coating, a smooth wear surface is formed by rubbing. Furthermore, as the void space between the squeezed and adhered CNT strands decreases, the resistance to structural deformation increases, thereby resulting in an increased frictional force and a wear pattern that becomes torn or forms a lump. Hence, the results obtained from this study corroborate that the friction and wear characteristics of CNT coatings can be enhanced through the absorption/dispersion of the contact pressure by controlling the stiffness of the nanomesh structure of CNT coatings.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.26-35
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• 2003

This study explains the effects of lubricant and surface treatment on hot forging die life. The mechanical and thermal load, and thermal softening which is happened by the high temperature of die, in hot and warm forging, cause die wear, heat checking and plastic deformation, etc. This study is fur the effects of solid lubricants and surface treatment condition for hot forging die. Because cooling effect and low friction are essential to the long life of dies, optimal surface treatment and lubricant are very important to improve die life for hot forging process. The main factors, which affect die hardness and heat transfer, are surface treatments and lubricants, which are related to thermal diffusion coefficient and heat transfer coefficient, etc. For verifying these effects, experiments are performed for hot ring compression test and heat transfer coefficient in various conditions as like different initial billet temperatures and different loads. The effects of lubricant and surface treatment for hot forging die life are explained by their thermal characteristics. The new developed technique in this study for predicting tool life can give more feasible means to improve the tool life in hot forging process.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.4
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• pp.5-13
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• 2004

This study explains the effects of lubricant and surface treatment on the life of hot forging dies. The thermal load and thermal softening, that occur when there is contact between the hotter billet and the cooler dies in hot forging, cause wear, thermal cracking and fatigue, and plastic deformation. Because the cooling effect and low friction are essential to the long life of dies, the proper selection of lubricant and surface treatment is very important in hot forging process. The two main factors that decide friction and heat transfer conditions are lubricant and surface treatment, which are directly related to friction factor and surface heat transfer coefficient. Experiments were performed for obtaining the friction factors and the surface heat transfer coefficients in different lubricants and surface treatments. For lubrication, oil-base and water-base graphite lubricants were used, and ion-nitride and carbon-nitride were used as surface treatment conditions. The methods for estimating die service life that are suggested in this study were applied to a finisher die during the hot forging of an automobile part. The new techniques developed in this study for estimating die service life can be used to develop more feasible ways to improve die service life in the hot forging process.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.28-36
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• 2007

A bulk amorphous NiTiZrSiSn powder produced using an inert gas atomization was sprayed by kinetic spraying process that is basically a solid-state deposition process onto a mild steel substrate. They were successfully overlaid onto the mild steel substrate. In order to evaluate the tribological behavior of the kinetic sprayed NiTiZrSiSn BMG (Bulk Metallic Glass) coatings, a partially crystallized coating and a fully crystallized coating were prepared by the isothermal heat treatments. Tribological behaviors were investigated in view of friction coefficient, hardness and amorphous phase fraction of coating layer. Surface morphologies and depth in the wear tracks were observed and measured by scanning electron microscope and alpha-step. From the examination of the scratch wear track microstructure, transition from the ductile like deformation (micro cutting) to the brittle deformation (micro fracturing) in the scratch groove was observed with the increase of the crystallinity.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.12
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• pp.8-15
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• 2021

Cold forging is a method in which molding is performed at room temperature. It has a high material recovery rate and dimensional precision and produces excellent surface quality, and it is mainly used for the production of bolted or housing products. The lifespan of cold forging molds is generally determined by the wear of the mold, plastic deformation of the mold, and fatigue strength. Cold forging molds are frequently damaged due to fatigue destruction rather than wear and plastic deformation in a high-temperature environment as it is molded at room temperature without preheating the raw material and mold. Based on the results analyzed through FEM, an effective mold structure design method was proposed by analyzing the changes in tensile and compressive stresses on molds according to the number of molds and reinforcement rings and comparing the product geometry and mold stress using three existing mold models.

• Corrosion Science and Technology
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• v.14 no.2
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• pp.59-63
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• 2015

Airless spray which is widely used for painting to ship blocks and hull sides is the coating method for attaching atomized paint material to the substrate using spray tip nozzle with compressed air. When the paint material which has high solid contents such as epoxy primer paint is atomized by passing through spray tip nozzle with high pressure, the nozzle composed of tungsten carbide(WC) undergoes the erosive wear, leading to widening of nozzle hole. The deformation of nozzle hole induces improper spray pattern and coating failures such as finger pattern and sagging because the conditions of spray pump pressure and paint flow rate for developing full spray pattern are changed. In this study, an appropriate replacement cycle of spray tip was predicted by measuring the erosive wear tendency as increasing the spraying time of epoxy primer paint.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1914-1922
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• 2002

Operating test of power-transmission plastic spur gears were performed inspecting both characteristics of friction-wear and endurance, and suggesting endurance improvement method that either drills internal holes of tooth or inserts metallic pin in the internal hole of tooth and verifying this newly-provided method. In case of acetal gears, amount of friction-wear is observed to increase by development of plastic deformation and increase of tooth stiffness due to brittle material property of acetal. To the contrary, in case of nylon gears, suggested method is shown to drop down the tooth temperature for about 3∼10$^{\circ}C$ than original gear, thus amount of wear is reduced by over 30% and operating lift prolonged by more than 200%. Hence, suggested method is proved to be practically applicable to the plastic gears made by soft polymers such as Nylon.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.805-810
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• 1997

In this paper the technique to predict tool were theoretically in the sheet metal shearing process is suggested. The were in sheet metal tool affects the tolerances of final parts, metal flows and costs of processes. In order to predict the tool were the deformation of workpiece during the process is analyzed by using non-isothermal finite element program. The ductile fracture criterion and the element kill method are also used to estimate if and where a fracture will occur and to investigate the features of the sheared surface in shearing process. Results obtained form finite element simulation such as node velocities and node forces are transformed into sliding velocity and normal pressure on tool monitoring points respectively. The monitoring points are automatically generated and the were rates on these points are accumulated during a process. It is assumed that the wear depth on the tool surface are linear function of the lot sizes based upon the known experimental results. The influence of clearance between die and punch upon tool wear is were is also discussed during the process.

• Journal of Drive and Control
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• v.15 no.1
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• pp.10-15
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• 2018

The hydraulic cylinder seals are used not only to protect leakage of the working fluids but also to prevent incoming of foreign particles into the system. Chromium plating is generally applied to improve corrosion and wear resistance. It has been noticed that sealing surface damage occurs due to the hard foreign/wear particles contained in the hydraulic oil. In this study, a three-bodied sliding contact problem related with a PTFE seal, a spherical particle and chrome-plated steel substrate is modeled to investigate the relations to wear mechanism. Using the nonlinear finite element software, MARC/MENTAT, the deformed shapes, the von Mises and first principal stress distributions with plating thickness were compared. The sealing surface was mainly abraded by hard particles embedded in the seal. The plastic deformation of the steel substrate decreased with thicker plating. Hence it could be more effective to coat the sealing surface of a hydraulic cylinder with a hard material such as TiN, TiC and DLC.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.251-256
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• 1999

"Ploughing" on the flank face of the tool in the metal cutting process is due to the tool in the metal cutting process is due to the finite edge radius of the tool and due to the development of flank wear. Because of the high stresses near the cutting edge, elastic-plastic deformation would be caused between the tool and the machined surface over a small area of the tool flank. The deformation would affect the roughness of the machined surface. Recently, some attempts have been made to predict the surface roughness, but elastic-plastic effect due to ploughing in the cutting process has not been considered. The research has analyzed mechanism of the ploughing of the cutting process using contact mechanics. Tool and workpiece material properties have been taken into account in the prediction of the surface roughness. The surface roughness has been simulated by the surface-shaping system. The results between experiment and simulation have been compared and analyzed. analyzed.